When wool is transported in bales to countries having cold climates, the wool is often frozen for considerable periods of the year. Similarly, when baled and dumped wool is placed in long term storage, the fibre develops a set, the extent of which depends on the factors of time, temperature, density and moisture content. It will be appreciated that baled wool which has a high set factor caused by low temperatures and/or long term storage is extremely difficult to open for further processing and the wool must dwell for considerable periods of time until the set in the wool eventually releases.
While it is known, for example from U.S. Pat. No. 233,288 Seeland and Russian Pat. No. 166588, to inject steam into frozen bales through a probe which penetrates the bale to speed the thawing process, thawing does not take place uniformly and difficulties are often experienced in obtaining adequate penetration of the probe due not only to the frozen state of the fibres but also to the high density of the fibres in the bale. Accordingly, the injection of steam in this manner is not a satisfactory solution to the problem of frozen bales and similarly does not provide a solution to the problem of opening high density, long term storage bales.
In our earlier patent referred to above, we have described a bale conditioning apparatus and method which constituted a significant improvement on the previously used conditioning methods, including the injection of steam as described above and the placing of bales in a warming room. However, further experimentation revealed that the forcing of a mixture of steam and moisture-laden heated air into the bales still resulted in bale residence times which were unacceptably long, that is, in excess of 20 minutes. It was found that the steam and moisture-laden heated air mixture built up in the bale and prevented further penetration of heat through the bale. The maximum allowable pressure (of the order of 120 kPa) was found to be insufficient to cause adequate penetration of the required heat front through the bale in an acceptable period of time. Any increase in the pressure of course resulted in an increase in temperature and, as has been found in the case of prior art steam injection methods, this often results in localized yellowing and oother damage to the wool fibres contained in the bale.